1. Field of the Invention
The invention relates to the field of aviation and, more particularly, the protection of a rotor shaft of a turbine engine against vibratory phenomena.
2. Description of the Related Art
A turbine engine mounted on an aircraft comprises one or more rotary shafts which provide the aircraft with thrust. Conventionally, a rotary shaft has a specific pulsation which corresponds to its first torsional mode. This torsional mode is characteristic of the geometry of the rotor shaft. In other words, the pulsation of the rotor shaft corresponds to an intrinsic vibratory frequency of the rotor shaft. Rotor shafts of one and the same type of turbine engine each have a specific pulsation, of the same order of magnitude, of between 20 and 50 Hz.
When the pulsation of the rotor shaft is excited, for example, when it receives a vibratory signal of which the frequency corresponds to its pulsation, the latter begins to resonate which leads to the generation of noises in the aircraft cabin and fatigue of the shaft.
This results in several drawbacks. First of all, the pilot of the aircraft, alerted by the noise, may ask for the turbine engine to be fully checked over, the aircraft then being immobilized on the ground which is a drawback. Moreover, the fatigue of the rotor shaft accelerates the wear of the mechanical elements surrounding the shaft, the elements therefore having to be replaced early, which increases maintenance costs.
In order to detect the inception of a resonance of the rotor shaft, several detection systems are known that make it possible to measure the vibratory response of the shaft due to an excitation, for example, by means of a tachymeter or of accelerometers as divulged in patent application FR2892516 by SNECMA. By virtue of such detection systems, which are preferably on board, it is possible to detect a resonance of the shaft.
Such detection systems are reliable but detection errors still remain. In order to improve the current detection systems, an immediate solution would consist in coupling a detection system comprising tachymeters with a detection system comprising accelerometers. Since these two systems measure the same type of signal (the vibratory response of the rotor shaft), such a coupling provides only a slight gain in reliability.